Regarding the separation of aromatic hydrocarbons BTX, i.e., benzene, toluene and xylene, from non-aromatic hydrocarbons, some catalytic conversion processes have been developed in the prior art. For example, U.S. Pat. No. 3,729,409 disclosed converting non-aromatic hydrocarbons to lower alkanes by hydrocracking reaction and then separating aromatic hydrocarbons from non-aromatic hydrocarbons through gas-liquid separation; U.S. Pat. No. 5,865,986 and U.S. Pat. No. 6,001,241 disclosed a process for upgrading naphtha fraction, wherein a zeolite-based catalyst is used in some reactors to improve the production of aromatic hydrocarbons; and CN1217892C disclosed a similar process, wherein reformate, pyrolysis gasoline and the like are upgrade to produce LPG and light aromatic hydrocarbons.
The acidic catalyst used in these catalytic conversion processes would deactivate quickly due to coke and/or carbon-deposition, although this can be alleviated by supporting the metals with high hydrogenation activity and the hydrogenation activity of the catalyst also can be adjusted by varying the amount and/or the distribution of the supported metals, however, too high hydrogenation activity on the metallic center may result in side reaction of saturation of aromatic rings. With this regard, U.S. Pat. No. 5,865,986 proposed to adjust the metallic activity with sulfur compounds. Furthermore, U.S. Pat. No. 6,001,241 proposed to use Pb or Bi to control the degree of hydrogenation.
On the other hand, the zeolite molecular sieve powder used for said catalysts are generally manufactured into shaped particles with certain mechanical strengths and shapes, and during this manufacture some binders e.g. oxides such as Al2O3, SiO2, TiO2 and the like as well as clay minerals are needed usually. This is because the shaped catalysts are widely used in industries and have to suffer from various stresses during its use, thus, sufficient mechanical strengths are necessary for ensuring the whole catalytic process to be conducted smoothly, otherwise if the shaped catalysts have poor mechanical strengths, some problems such as the lines being blocked by fine powders, the liquid being distributed unevenly, the pressure drop being increased and the like would be introduced, so as to lead to poor catalytic efficiency, and even a unexpected shut-down in worse case.
However, introduction of binders during shaping the zeolite powders would reduce the concentration of effective components in the zeolite particles, resulting in reduced effective surface area, and thus the adsorption value would be reduced. This is because some binders would enter into part of channels of the zeolite or block part of pores of the zeolite, thus limiting the diffusion, resulting in poor adsorption ability and adsorption selectivity as well as reduced rates of adsorption and desorption, further the reduced activity and selectivity in the catalytic reactions; furthermore, undesired side reactions may be initiated in the presence of binders.
Regarding the above-mentioned disadvantages in connection with the introduction of binders during shaping the zeolite powders, the inventors have tried to develop a process for producing a binder-free zeolite, c.f. CN1915820A, which is incorporated herein by reference. The binder-free zeolite means that the shaped zeolite particles do not comprise inert binders, thus having high concentration of zeolite and large available surface area; furthermore, better properties in adsorption separation and ion exchange as well as better catalytic properties in some reactions are shown.
Based on the above-mentioned finding, the inventors further tried to develop a catalyst using said binder-free zeolite particles as support. Said catalyst has higher catalytic activity and stability and can be used for producing light aromatic hydrocarbons and light alkanes from hydrocarbonaceous feedstock.